U.S. Pat. No. 3,469,188 (Hall) describes a circuit for use with lightning arresters to provide a measure of the grading current and leakage current associated with the arresters as well as to count the number of surges occurring through the arresters. The circuit employs a series gapped voltage dependent nonlinear resistor and a second nonlinear resistor in series with a charging capacitor for the operation of a cyclometer.
When zinc oxide varistors are used within the lightning arrester assembly, no gaps are generally required and a steady state leakage current continuously passes through the arresters to ground. Replacing the two Thyrite varistors and the series gap disclosed within the aforementioned U.S. Patent, with a single zinc oxide varistor, allows the leakage current to be read on a similarly arranged meter and also allows the number of surges to be recorded on a similar cyclometer arrangement. One of the problems involved with the discharge counter and grading current measuring means described in the aforementioned U.S. Patent is the occurrence of reverse current effects immediately subsequent to a surge current which often causes the capacitor associated with the cyclometer to discharge before the cyclometer can become activated. Another problem involved with the aforementioned circuit is the erroneous indication of the magnitude of the leakage current, caused by high frequency components in the leakage current through the measuring circuit. These high frequency current components can charge the capacitor sufficiently to drive the meter and give a false indication of the leakage current.
The purpose of the instant invention is to provide a circuit for surge arresters which reliably provides an indication of the leakage current and which accurately records the number of voltage surges through the arresters.